Automatic temperature regulation



Oct. 6, 1942. c. c. LEVY Filed Feb. 26, 1941 Patented Oct. 6, 1942 UNI-TED ASTATES PATENT OFFICE Cyril C. Levy, Pittsburgh, Pa., assigner toiWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania A Application February 26, 1941, Serial No. 380,679

Claims.

Ihis invention relates to automatic temperature regulators for controlling the iiow of electric power to heating devices, such as resistor type furnaces, or the like.

It is an object of the invention to provide a 5 variable impedance device in the furnace load circuit and means for controlling said variable impedance device including a control influence that is responsive to the furnace temperature and a control influence that is responsive to an electrical characteristic of the circuit supplying the furnace.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention, reil5 erence being had to the accompanying drawing. in which apparatus and circuits illustrating a diagrammatic view of the described embodiment are shown.

Referring to the drawing, an alternating current supply circuit is provided represented by supply conductors I and 2 and connected to the primary winding 3 of a power transformer having a secondary winding 4 that is connected tothe load element 5 of a furnace. This circuit is traced 2.5

from winding 4 through conductor 6, load element 5, conductor 1, and windings 8 and 3 of a variable impedance device II to the other terminal of the winding 4,. The device II is shown as a saturable reactor having three winding legs, so

the two outer legs accommodating the alternating current windings 3 and 9, and the center winding leg accommodating a controlling winding I2 that is supplied with unidirectional energy through a circuit including a. transformer I3 and grid conu trolled rectifier tubes I5 and I3. The primary winding of thetransformer I3 is connected to the alternating source conductors I and 2, and the opposite ends of the secondary winding of the transformer are connected to anodes I4 of 40 the tube-rectifiers I5 and I6. 'I'he rectiiiers are also provided with cathodes I1 that are connected together and through conductor I8, the winding I2, and conductor I9 to the midpoint 20 of the secondary winding of the transformer I3. The 45 arm 24, conductor 25, a portion of a resistor 28, 50

and conductor 21 to the cathode I1. A dry type rectifier 28 is provided for supplying a unidirectional voltage through conductors 29 and 3I across the resistor 26. The alternating current secondary winding of a transformer 32, the primary winding of which is connected to the alternating current supply conductors I and 2. The potentiometer resistor 23 is supplied with unidirectional voltage through conductors 33 and 34 from a dry type rectifier 35, the alternating current terminals of which are connected by conductors 35 and 31 to points 38 and 39, respectively, corresponding tc the terminals of the load resistor 5.

A control instrument is provided including a thermocouple so located as to be responsive to the temperature of the furnace heated by the load element 5 and connected for supplying a varying potential, depending upon the furnace temperature, to a circuit including conductor 4I, rheostat contact element 42, a portion of a potentiometer resistor 43, conductors 44 and 45, galvanometer 46, and conductor 41. A standard battery cell 43 is provided for supplying current through the resistor 43 in the local circuit including conductors 44 and 43.

Means for simultaneously shifting the rheostat contact members 42 and 24 along resistors 43 and 23, respectively, is provided and is here shown as a traveling nut 5I mounted on a threaded shaft 52 that is controlled by a motor having an armature winding 53 and two field windings 54 and 53 through the one or the other of which a circuit may be completed by the galvanomer 48 from a source of energy shown as a battery 56 to effect operation of the motor in the one or the other direction in a well known manner.

If the furnace is in operation and the temperature of the furnace is at its desired value, the voltage developed by the thermocouple 43 will be .such that in the above traced circuit from the thermocouple 43 as a source, the voltage between the rheostat contact member 42 and the conductor 44 across the included portion of the resistor 43 will just balance the voltage drop across the same portion of the resistor 43 impressed from the standard battery cell 48 in the local circuit from the battery cell 48 including the entire resistor 43. The two sources 48 and 40 are so connected in circuit that the voltages are in opposition across the portion of the resistor between the contact member 42 and the conductor 44. If now for any reason the temperature cf the furnace decreases, the voltage developed by the thermocouple 40 will correspondingly decrease so that there may be a voltage unbalance between the voltage impressed by the thermocouple and that impressed by the cell 4l across the portion of the terminals of the rectifier 28 'are connected to the u resistor 43 between the rheostat contact member 

